T. Hannken et al., ANGIOTENSIN II-MEDIATED EXPRESSION OF P27(KIP1) INDUCTION OF CELLULARHYPERTROPHY IN RENAL TUBULAR CELLS DEPEND ON THE GENERATION OF OXYGENRADICALS, Kidney international, 54(6), 1998, pp. 1923-1933
Background. Angiotensin II (Ang II) induces hypertrophy of cultured pr
oximal tubular cells. We have previously demonstrated that this Ang II
-mediated hypertrophy occurs in the G(1)-phase of the cell cycle and d
epends on the induction of p27(Kip1),an inhibitor of G(1)-phase cyclin
/cyclin-dependent kinase complexes. The present study was undertaken t
o investigate whether Ang II may stimulate superoxide anions (O-2(.))
formation in cultured LLC-PK1 and cultured mouse proximal tubule (MCT)
cells, and to gain further insight into a potential relationship betw
een O-2(.) and cell cycle regulation. Methods. Reactive oxygen species
were measured with the lucigenin method in intact cells. The effects
of various inhibitors were tested on Ang II-induced O-2(.) production.
Cells were transiently transfected with phosphorothioate-modified rat
p22phox antisense oligonucleotides to investigate the potential role
of NAD(P)H oxidase. Expression of p22phox mRNA after Ang II-treatment
was detected with Northern blots. Incorporation of [H-3]leucine into d
e novo synthesized proteins was used as a parameter of cell hypertroph
y. Expression of p27(Kip1) was evaluated in cell lysates by Western bl
otting. Results. Ang II stimulated the accumulation of O-2(.) in tubul
ar cells; however, an addition of two different antioxidants completel
y abolished measurable O-2(.). This effect was transduced by angiotens
in receptor type-1 (AT(1)) and was inhibited by a flavoprotein inhibit
or (DIP) or p22phox antisense oligonucleotides, indicating the involve
ment of membrane NAD(P)H oxidase. Ang II-stimulated de novo protein sy
nthesis was attenuated by DIP, antioxidants, and p22phox antisense oli
gonucleotides. The Ang II-induced expression of p27(Kip1) protein and
cellular hypertrophy were reduced by similar treatments. Generation of
O-2(.) by xanthine supplementation also stimulated p27(Kip1) expressi
on and induced hypertrophy in LLC-PK1 cells. Conclusion. This study pr
ovides the first evidence, to our knowledge, that Ang II induces O-2.
in cultured tubular cells. Ang II-mediated activation of membrane boun
d NAD(P)H oxidase, probably by an increase in p22phox transcripts, is
likely responsible for this induction. Generation of O-2(.) subsequent
ly induces p27(Kip1) expression and stimulates hypertrophy, suggesting
a novel mechanism of how Ang II can modulate cell cycle regulation.